Dephasing

Dephasing is a name for the mechanism that recovers classical behavior from a quantum system. It is an important effect in condensed matter physics, particularly in the study of mesoscopic devices. The reason can be understood easily if we can see conduction in metals as a typical classical phenomenon with quantum effects all embedded into an effective mass that can be computed quantum mechanically as also happens to resistance that can be seen as a scattering effect of conduction electrons. When the temperature is lowered and the dimensions of the device are meaningfully reduced, this classical behavior should disappear and the laws of quantum mechanics should govern the behavior of conducting electrons seen as waves that ballistically move inside the conductor without any kind of dissipation. Most of the time this is what one observes. But it appeared as a surprise to uncover that the so called dephasing time, that is the time it takes for the conducting electrons to lose their quantum behavior, becomes finite rather than infinite when the temperature approaches zero in mesoscopic devices violating the expectations of the theory of Altshuler, Aronov and Khmelnitskii (see citation below). This kind of saturation of the dephasing time at low temperatures is presently an open problem even as several proposals have been put forward.